It is known to prepare greases from base oil, a thickener and optionally other performance additives for example antioxidants or antiwear agents. Polymers have also been added to greases in an attempt to improve the performance characteristics of the grease, for example, polymers have been employed to decrease water wash-off, to increase water repellency, to decrease oil separation, to increase dropping points or cone penetration and as thickeners. Often the polymers of polymethacrylates or polyolefins are added to grease. Typically these polymers are incorporated in the base oil and act as a viscosity modifier. However, the polymers have limited interaction with the thickener. This results in the grease being more susceptible to the effects of water, for example, water wash-off or decreased water repellency. Producing greases with poor water wash-off or water repellency decreases the longevity of grease and increases wear on the surface being lubricated.
U.S. Pat. No. 5,000,862 discloses a process for lubricating and protecting bearings in a steel process mill. The process caster rollers have improved longevity, rust and corrosion by using grease containing a polymethacrylate additive. The polymethacrylate additive, imparts improved water resistance and reduced water wash-off. The polymethacrylate is not functionalised and does not interact with the base oil and thickener used to form the greases.
U.S. Pat. No. 4,929,371 discloses the use of polymers additives in greases selected from polyurethanes, polyoxides, polyamines, polyacrylamides, polyvinyl alcohols, ethylene vinyl acetates, polyvinyl acetates, polyvinyl pyrrolidones, polyolefins, polyolefin arylenes, polyarylenes and polymethacrylates. The polymers are thermally stable and minimise high temperature oxidation, corrosion, thermal breakdown, detrimental polymerisation of the grease and lacquering. The polymers are hydrophobic and extend the useful life of the greases. The polymers are unfunctionalised except when the polymers can be reacted with boric acid or boron containing compounds resulting in a borated polymer.
Chinese Patent Application 87105053A discloses lithium greases prepared by saponification of C12-C24 fatty acid and lithium hydroxide, a synthetic or mineral oil and an additive package containing polymethacrylate at 1 wt % of the grease composition. The polymethacrylate is not functionalised and does not interact with the base oil and thickener used to form greases.
U.S. Pat. No. 4,668,412 discloses polymers which have been functionalised and are capable of use in lubricating oils containing at least one (meth) acrylate monomer, a dicarboxylic acid anhydride, an amine and a functionalising Mannich base. The first and second (meth) acrylate esters are derived from alcohols with 10 to 16 carbon atoms, and 12 to 18 carbon atoms respectively. The dicarboxylic acid anhydride is maleic anhydride or derivatives thereof. The amine can be primary or secondary functionalised. The Mannich base is formed from the reaction of phenols, aldehydes and polyamines through the nitrogen of the polymer amine group.
It would be desirable to have an oil of lubricating viscosity containing polymers suitable for greases that are capable of imparting improved thickening, decreased water wash-off, increased water repellence, prolonged longevity and decreased wear.
The present invention provides a grease composition containing polymers capable of improving greases by imparting improved water wash-off and water repellence. The invention further provides a grease composition containing polymers capable of improving thickening. The invention further provides a grease composition containing polymers capable of decreasing wear and increasing longevity.